The present invention relates generally to degradable diverting agents, and more particularly to degradable diverting agents that include a combination or blend of polylactic acid and an acid-soluble hard particulate.
Diverting agents may be used in a variety of subterranean treatments. Such treatments include, but are not limited to, drilling, stimulation treatments (e.g., fracturing treatments, matrix acidizing treatments), and cementing operations. For example, after a well bore is drilled and completed in a subterranean producing zone, it is often necessary to introduce a treatment fluid into the zone. For example, a producing zone can be stimulated by introducing an aqueous acid solution into the matrix of a producing zone to dissolve formation material or materials near the wellbore which impede well productivity, and thereby increase its porosity and permeability. This results in an increase in the production of hydrocarbons therefrom. To insure that the producing zone is contacted by the treating fluid uniformly, a particulate solid diverting agent may be placed in the zone to direct the placement of a desired treatment fluid. One technique has been to pack the diverting agent in perforation tunnels extending from the wellbore into the subterranean zone. The diverting agent in the perforation tunnels causes the treatment fluid introduced therein to be uniformly distributed between all of the perforations whereby the subterranean zone is uniformly treated.
Traditional diverting agents may be grouped into two classifications. Such classifications include viscous fluid diverting agents and physical/mechanical diverting agents. In the former, typically, a relatively high viscosity fluid flows into a subterranean zone, creating a resistance that causes subsequent treatment fluids to be diverted to other portions of the formation. Such diversion methods are considered relatively easy to implement, but are generally thought not to be as effective as diverting agents that introduce a physical or mechanical barrier. Additionally, high temperatures associated with wells of greater depth lead to increased instability of such viscosified fluids.
Diverting agents that work by forming a physical barrier to flow may include perforation ball sealers and particulate diverters. Commonly used particulate diverting agents may be non-degradable or degradable. Most commercially available ball sealers are either a solid material or will have a solid, rigid core including materials that are stable under downhole conditions, and thus, following a treatment, need to be recovered from the wellbore or otherwise removed from the treatment interval. This clean-up activity delays, complicates and adds expense to the well treatment process. An additional limitation of the use of perforation ball sealers is that they are only applicable in cased, perforated well bores; they are not applicable to other well completion scenarios such as open hole or with a slotted liner.
Particulate diverting agents often are suspended or dissolved in a carrier fluid until that fluid is saturated with the agents and excess material exists, and this fluid is introduced to the subterranean formation during the stimulation treatment. Traditional examples of particulate diverting agents are inorganic materials such as rock salts and polymeric materials such as starch and polyesters. The particulate materials typically form a seal in the subterranean formation (e.g., by packing off perforation tunnels, plating off a formation surface, plating off a hole behind a slotted liner, or packing along the surface of a hydraulic fracture), causing the treatment fluid to be diverted uniformly to other portions of the formation. If non-degradable diverting agents are used, the particulate solid diverting agent often is removed from the perforation tunnels or hole to allow the maximum flow of produced fluids that comprise hydrocarbons from the subterranean zone to flow into the wellbore. Subsequent operations necessary for removing such diverting agents often entail considerable time and expense and added complications.
Thus, there is a continuing need for improved methods and compositions for degradable diverting agents.